More Letters of Charles Darwin Volume II
by
Charles Darwin
Part 6 out of 14
the pollen on the upper petals, and so not leave it on stigma. It is to
know whether I have rightly interpreted the structure of this whole flower
that I am so curious to see how insects act. Small insects, I daresay,
would crawl in and out and do nothing. I hope that I shall not have
wearied you with these details.
If you would like to see a pretty and curious little sight, look to Orchis
pyramidalis, and you will see that the sticky glands are congenitally
united into a saddle-shaped organ. Remove this under microscope by pincers
applied to foot-stalk of pollen-mass, and look quickly at the spontaneous
movement of the saddle-shaped organs and see how beautifully adapted to
seize proboscis of moth.
LETTER 597. TO J.D. HOOKER
December 4th [1860].
Many thanks about Apocynum and Meyen.
The latter I want about some strange movements in cells of Drosera, which
Meyen alone seems to have observed. (597/1. No observations of Meyen are
mentioned in "Insectivorous Plants.) It is very curious, but Trecul
disbelieves that Drosera really clasps flies! I should very much wish to
talk over Drosera with you. I did chloroform it, and the leaves which were
already expanded did not recover thirty seconds of exposure for three days.
I used the expression weight for the bit of hair which caused movement and
weighed 1/78000 of a grain; but I do not believe it is weight, and what it
is, I cannot after many experiments conjecture. (597/2. The doubt here
expressed as to whether the result is due to actual weight is interesting
in connection with Pfeffer's remarkable discovery that a smooth object in
contact with the gland produces no effect if the plant is protected from
all vibration; on an ordinary table the slight shaking which reaches the
plant is sufficient to make the body resting on the gland tremble, and thus
produce a series of varying pressures--under these circumstances the gland
is irritated, and the tentacle moves. See Pfeffer, "Untersuchungen aus d.
bot. Institut zu Tubingen," Volume I., 1885, page 483; also "Insectivorous
Plants," Edition II., page 22.) The movement in this case does not depend
on the chemical nature of substance. Latterly I have tried experiments on
single glands, and a microscopical atom of raw meat causes such rapid
movement that I could see it move like hand of clock. In this case it is
the nature of the object. It is wonderful the rapidity of the absorption:
in ten seconds weak solution of carbonate of ammonia changes not the
colour, but the state of contents within the glands. In two minutes thirty
seconds juice of meat has been absorbed by gland and passed from cell to
cell all down the pedicel (or hair) of the gland, and caused the sap to
pass from the cells on the upper side of the pedicel to the lower side, and
this causes the curvature of the pedicel. I shall work away next summer
when Drosera opens again, for I am much interested in subject. After the
glandular hairs have curved, the oddest changes take place--viz., a
segregation of the homogeneous pink fluid and necessary slow movements in
the thicker matter. By Jove, I sometimes think Drosera is a disguised
animal! You know that I always so like telling you what I do, that you
must forgive me scribbling on my beloved Drosera. Farewell. I am so very
glad that you are going to reform your ways; I am sure that you would have
injured your health seriously. There is poor Dana has done actually
nothing--cannot even write a letter--for a year, and it is hoped that in
another YEAR he may quite recover.
After this homily, good night, my dear friend. Good heavens, I ought not
to scold you, but thank you, for writing so long and interesting a letter.
LETTER 598. TO E. CRESY.
Down, December 12th [1860?].
After writing out the greater part of my paper on Drosera, I thought of so
many points to try, and I wished to re-test the basis of one large set of
experiments, namely, to feel still more sure than I am, that a drop of
plain water never produces any effect, that I have resolved to publish
nothing this year. For I found in the record of my daily experiments one
suspicious case. I must wait till next summer. It will be difficult to
try any solid substances containing nitrogen, such as ivory; for two quite
distinct causes excite the movement, namely, mechanical irritation and
presence of nitrogen. When a solid substance is placed on leaf it becomes
clasped, but is released sooner than when a nitrogenous solid is clasped;
yet it is difficult (except with raw meat and flies) to be sure of the
result, owing to differences in vigour of different plants. The last
experiments which I tried before my plants became too languid are very
curious, and were tried by putting microscopical atoms on the gland itself
of single hairs; and it is perfectly evident that an atom of human hair,
1/76000 of a grain (as ascertained by weighing a length of hair) in weight,
causes conspicuous movement. I do not believe (for atoms of cotton thread
acted) it is the chemical nature; and some reasons make me doubt whether it
is actual weight; it is not the shadow; and I am at present, after many
experiments, confounded to know what the cause is. That these atoms did
really act and alter the state of the contents of all the cells in the
glandular hair, which moved, was perfectly clear. But I hope next summer
to make out a good deal more...
LETTER 599. TO J.D. HOOKER.
Down, May 14th [1861].
I have been putting off writing from day to day, as I did not wish to
trouble you, till my wish for a little news will not let me rest...
I have no news to tell you, for I have had no interesting letters for some
time, and have not seen a soul. I have been going through the "Cottage
Gardener" of last year, on account chiefly of Beaton's articles (599/1.
Beaton was a regular contributor to the "Cottage Gardener," and wrote
various articles on cross breeding, etc., in 1861. One of these was in
reply to a letter published in the "Cottage Gardener," May 14th, 1861, page
112, in which Darwin asked for information as to the Compositae and the
hollyhock being crossed by insect visitors. In the number for June 8th,
1861, page 211, Darwin wrote on the variability of the central flower of
the carrot and the peloria of the central flower in Pelargonium. An
extract from a letter by Darwin on Leschenaultia, "Cottage Gardener," May
28th, 1861, page 151, is given in Letter 590, note.); he strikes me as a
clever but d--d cock-sure man (as Lord Melbourne said), and I have some
doubts whether to be much trusted. I suspect he has never recorded his
experiment at the time with care. He has made me indignant by the way he
speaks of Gartner, evidently knowing nothing of his work. I mean to try
and pump him in the "Cottage Gardener," and shall perhaps defend Gartner.
He alludes to me occasionally, and I cannot tell with what spirit. He
speaks of "this Mr. Darwin" in one place as if I were a very noxious
animal.
Let me have a line about poor Henslow pretty soon.
(599/2. In a letter of May 18th, 1861, Darwin wrote again:--)
By the way, thanks about Beaton. I have now read more of his writings, and
one answer to me in "Cottage Gardener." I can plainly see that he is not
to be trusted. He does not well know his own subject of crossing.
LETTER 600. TO J.D. HOOKER.
(600/1. Part of this letter has been published in "Life and Letters,"
III., page 265.)
2, Hesketh Crescent, Torquay [1861].
...The beauty of the adaptation of parts seems to me unparalleled. I
should think or guess [that] waxy pollen was most differentiated. In
Cypripedium, which seems least modified, and a much exterminated group, the
grains are single. In all others, as far as I have seen, they are in
packets of four; and these packets cohere into many wedge-formed masses in
Orchis, into eight, four, and finally two. It seems curious that a flower
should exist which could, at most, fertilise only two other flowers, seeing
how abundant pollen generally is; this fact I look at as explaining the
perfection of the contrivance by which the pollen, so important from its
fewness, is carried from flower to flower. By the way, Cephalanthera has
single pollen-grains, but this seems to be a case of degradation, for the
rostellum is utterly aborted. Oddly, the columns of pollen are here kept
in place by very early penetration of pollen-tubes into the edge of the
stigma; nevertheless, it receives more pollen by insect agency. Epithecia
[Dichaea] has done me one good little turn. I often speculated how the
caudicle of Orchis had been formed. (600/2. The gradation here suggested
is thoroughly worked out in the "Fertilisation of Orchids," Edition I.,
page 323, Edition II., page 257.) I had noticed slight clouds in the
substance half way down; I have now dissected them out, and I find they are
pollen-grains fairly embedded and useless. If you suppose the pollen-
grains to abort in the lower half of the pollinia of Epipactis, but the
parallel elastic threads to remain and cohere, you have the caudicle of
Orchis, and can understand the few embedded and functionless pollen-grains.
I must not look at any more exotic orchids: hearty thanks for your offer.
But if you would make one single observation for me on Cypripedium, I
should be glad. Asa Gray writes to me that the outside of the pollen-
masses is sticky in this genus; I find that the whole mass consists of
pollen-grains immersed in a sticky brownish thick fluid. You could tell by
a mere lens and penknife. If it is, as I find it, pollen could not get on
the stigma without insect aid. Cypripedium confounds me much. I
conjecture that drops of nectar are secreted by the surface of the labellum
beneath the anthers and in front of the stigma, and that the shield over
the anthers and the form of labellum is to compel insects to insert their
proboscis all round both organs. (600/3. This view was afterwards given
up.) It would be troublesome for you to look at this, as it is always
bothersome to catch the nectar secreting, and the cup of the labellum gets
filled with water by gardener's watering.
I have examined Listera ovata, cordata, and Neottia nidus avis: the pollen
is uniform; I suspect you must have seen some observation founded on a
mistake from the penetration and hardening of sticky fluid from the
rostellum, which does penetrate the pollen a little.
It is mere virtue which makes me not wish to examine more orchids; for I
like it far better than writing about varieties of cocks and hens and
ducks. Nevertheless, I have just been looking at Lindley's list in the
"Vegetable Kingdom," and I cannot resist one or two of his great division
of Arethuseae, which includes Vanilla. And as I know so well the Ophreae,
I should like (God forgive me) any one of the Satyriadae, Disidae and
Corycidae.
I fear my long lucubrations will have wearied you, but it has amused me to
write, so forgive me.
LETTER 601. TO J.D. HOOKER.
(601/1. Part of the following letter is published in the "Life and
Letters," the remainder, with the omission of part bearing on the Glen Roy
problem, is now given as an example of the varied botanical assistance
Darwin received from Sir Joseph Hooker. For the part relating to Verbascum
see the "Variation of Animals and Plants," Edition II., 1875, Volume II.,
page 83. The point is that the white and yellow flowered plants which
occur in two species of Verbascum are undoubted varieties, yet "the
sterility which results from the crossing of the differently coloured
varieties of the same species is fully as great as that which occurs in
many cases when distinct species are crossed."
The sterility of the long-styled form (B) of Linum grandiflorum, with its
own pollen is described in "Forms of Flowers," Edition II., page 87: his
conclusions on the short-styled form (A) differ from those in the present
letter.)
September 28th [1861].
I am going to beg for help, and I will explain why I want it.
You offer Cypripedium; I should be very glad of a specimen, and of any
good-sized Vandeae, or indeed any orchids, for this reason: I never
thought of publishing separately, and therefore did not keep specimens in
spirits, and now I should be very glad of a few woodcuts to illustrate my
few remarks on exotic orchids. If you can send me any, send them by post
in a tin canister on middle of day of Saturday, October 5th, for Sowerby
will be here.
Secondly: Have you any white and yellow varieties of Verbascum which you
could give me, or propagate for me, or LEND me for a year? I have resolved
to try Gartner's wonderful and repeated statement, that pollen of white and
yellow varieties, whether used on the varieties or on DISTINCT species, has
different potency. I do not think any experiment can be more important on
the origin of species; for if he is correct we certainly have what Huxley
calls new physiological species arising. I should require several species
of Verbascum besides the white and yellow varieties of the same species.
It will be tiresome work, but if I can anyhow get the plants, it shall be
tried.
Thirdly: Can you give me seeds of any Rubiaceae of the sub-order
Cinchoneae, as Spermacoce, Diodia, Mitchella, Oldenlandia? Asa Gray says
they present two forms like Primula. I am sure that this subject is well
worth working out. I have just almost proved a very curious case in Linum
grandiflorum which presents two forms, A and B. Pollen of A is perfectly
fertile on stigma of A. But pollen of B is absolutely barren on its own
stigma; you might as well put so much flour on it. It astounded me to see
the stigmas of B purple with its own pollen; and then put a few grains of
similar-looking pollen of A on them, and the germen immediately and always
swelled; those not thus treated never swelling.
Fourthly: Can you give me any very hairy Saxifraga (for their functions)
[i.e. the functions of the hairs]?
I send you a resume of my requests, to save you trouble. Nor would I ask
for so much aid if I did not think all these points well worth trying to
investigate.
My dear old friend, a letter from you always does me a world of good. And,
the Lord have mercy on me, what a return I make.
LETTER 602. TO J.D. HOOKER.
Down, October 4th [1861].
Will you have the kindness to read the enclosed, and look at the diagram.
Six words will answer my question. It is not an important point, but there
is to me an irresistible charm in trying to make out homologies. (602/1.
In 1880 he wrote to Mr. Bentham: "It was very kind of you to write to me
about the Orchideae, for it has pleased me to an extreme degree that I
could have been of the least use to you about the nature of the parts."--
"Life and Letters," III., page 264.) You know the membranous cup or
clinandrum, in many orchids, behind the stigma and rostellum: it is formed
of a membrane which unites the filament of the normal dorsal anther with
the edges of the pistil. The clinandrum is largely developed in Malaxis,
and is of considerable importance in retaining the pollinia, which as soon
as the flower opens are quite loose.
The appearance and similarity of the tissues, etc., at once gives suspicion
that the lateral membranes of the clinandrum are the two other and
rudimentary anthers, which in Orchis and Cephalanthera, etc., exist as mere
papillae, here developed and utilised.
Now for my question. Exactly in the middle of the filament of the normal
anther, and exactly in the middle of the lateral membrane of the
clinandrum, and running up to the same height, are quite similar bundles of
spiral vessels; ending upwards almost suddenly. Now is not this structure
a good argument that I interpret the homologies of the sides of clinandrum
rightly? (602/2. Though Robert Brown made use of the spiral vessels of
orchids, yet according to Eichler, "Bluthendiagramme," 1875, Volume I.,
page 184, Darwin was the first to make substantial additions to the
conclusions deducible from the course of the vessels in relation to the
problem of the morphology of these plants. Eichler gives Darwin's diagram
side by side with that of Van Tieghem without attempting to decide between
the differences in detail by which they are characterised.)
I find that the great Bauer does not draw very correctly! (602/3. F.
Bauer, whom Pritzel calls "der grosste Pflanzenmaler." The reference is to
his "Illustrations of Orchidaceous Plants, with Notes and Prefatory Remarks
by John Lindley," London, 1830-38, Folio. See "Fertilisation of Orchids,"
Edition II., page 82.) And, good Heavens, what a jumble he makes on
functions.
LETTER 603. TO J.D. HOOKER.
Down, October 22nd. [1861].
Acropera is a beast,--stigma does not open, everything seems contrived that
it shall NOT be anyhow fertilised. There is something very odd about it,
which could only be made out by incessant watching on several individual
plants.
I never saw the very curious flower of Canna; I should say the pollen was
deposited where it is to prevent inevitable self-fertilisation. You have
no time to try the smallest experiment, else it would be worth while to put
pollen on some stigmas (supposing that it does not seed freely with you).
Anyhow, insects would probably carry pollen from flower to flower, for Kurr
states the tube formed by pistil, stamen and "nectarblatt" secretes (I
presume internally) much nectar. Thanks for sending me the curious flower.
Now I want much some wisdom; though I must write at considerable length,
your answer may be very brief.
(FIGURE 8.--FLORAL DIAGRAM OF AN ORCHID.
The "missing bundle" could not be found in some species.)
In R. Brown's admirable paper in the "Linnean Transacts." (603/4. Volume
XVI., page 685.) he suggests (and Lindley cautiously agrees) that the
flower of orchids consists of five whorls, the inner whorl of the two
whorls of anthers being all rudimentary, and when the labellum presents
ridges, two or three of the anthers of both whorls [are] combined with it.
In the ovarium there are six bundles of vessels: R. Brown judged by
transverse sections. It occurred to me, after what you said, to trace the
vessels longitudinally, and I have succeeded well. Look at my diagram
[Figure 8] (which please return, for I am transported with admiration at
it), which shows the vessels which I have traced, one bundle to each of
fifteen theoretical organs, and no more. You will see the result is
nothing new, but it seems to confirm strongly R. Brown, for I have
succeeded (perhaps he did, but he does not say so) in tracing the vessels
belonging to each organ in front of each other to the same bundle in the
ovarium: thus the vessels going to the lower sepal, to the side of the
labellum, and to one stigma (when there are two) all distinctly branch from
one ovarian bundle. So in other cases, but I have not completely traced
(only seen) that going to the rostellum. But here comes my only point of
novelty: in all orchids as yet looked at (even one with so simple a
labellum as Gymnadenia and Malaxis) the vessels on the two sides of the
labellum are derived from the bundle which goes to the lower sepal, as in
the diagram. This leads me to conclude that the labellum is always a
compound organ. Now I want to know whether it is conceivable that the
vessels coming from one main bundle should penetrate an organ (the
labellum) which receives its vessels from another main bundle? Does it not
imply that all that part of the labellum which is supplied by vessels
coming from a lateral bundle must be part of a primordially distinct organ,
however closely the two may have become united? It is curious in
Gymnadenia to trace the middle anterior bundle in the ovarium: when it
comes to the orifice of the nectary it turns and runs right down it, then
comes up the opposite side and runs to the apex of the labellum, whence
each side of the nectary is supplied by vessels from the bundles, coming
from the lower sepals. Hence even the thin nectary is essentially, I
infer, tripartite; hence its tendency to bifurcation at its top. This view
of the labellum always consisting of three organs (I believe four when
thick, as in Mormodes, at base) seems to me to explain its great size and
tripartite form, compared with the other petals. Certainly, if I may trust
the vessels, the simple labellum of Gymnadenia consists of three organs
soldered together. Forgive me for writing at such length; a very brief
answer will suffice. I am desperately interested in the subject: the
destiny of the whole human race is as nothing to the course of vessels of
orchids...
What plant has the most complex single stigma and pistil? The most complex
I, in my ignorance, can think of is in Iris. I want to know whether
anything beats in modification the rostellum of Catasetum. To-morrow I
mean to be at Catasetum. Hurrah! What species is it? It is wonderfully
different from that which Veitch sent me, which was C. saccatum.
According to the vessels, an orchid flower consists of three sepals and two
petals free; and of a compound organ (its labellum), consisting of one
petal and of two (or three) modified anthers; and of a second compound body
consisting of three pistils, one normal anther, and two modified anthers
often forming the sides of the clinandrum.
LETTER 604. TO JOHN LINDLEY.
(604/1. It was in the autumn of 1861 that Darwin made up his mind to
publish his Orchid work as a book, rather than as a paper in the Linnean
Society's "Journal." (604/2. See "Life and Letters," III., page 266.)
The following letter shows that the new arrangement served as an incitement
to fresh work.)
Down, October 25th [1861?]
Mr. James Veitch has been most generous. I did not know that you had
spoken to him. If you see him pray say I am truly grateful; I dare not
write to a live Bishop or a Lady, but if I knew the address of "Rucker"?
and might use your name as introduction, I might write. I am half mad on
the subject. Hooker has sent me many exotics, but I stopped him, for I
thought I should make a fool of myself; but since I have determined to
publish I much regret it.
(FIGURE 9.--HABENARIA CHLORANTHA (Longitudinal course of bundles).)
(605/1. The three upper curved outlines, two of which passing through the
words "upper sepal," "upper petal," "lower sepal," were in red in the
original; for explanation see text.)
LETTER 605. TO J.D. HOOKER.
(605/2. The following letter is of interest because it relates to one of
the two chief difficulties Darwin met with in working out the morphology of
the orchid flower. In the orchid book (605/3. Edition I., page 303.) he
wrote, "This anomaly [in Habenaria] is so far of importance, as it throws
some doubt on the view which I have taken of the labellum being always an
organ compounded of one petal and two petaloid stamens." That is to say,
it leaves it open for a critic to assert that the vessels which enter the
sides of the labellum are lateral vessels of the petal and do not
necessarily represent petaloid stamens. In the sequel he gives a
satisfactory answer to the supposed objector.)
Down, November 10th, [1861].
For the love of God help me. I believe all my work (about a fortnight) is
useless. Look at this accursed diagram (Figure 9) of the butterfly-orchis
[Habenaria], which I examined after writing to you yesterday, when I
thought all my work done. Some of the ducts of the upper sepal (605/4.
These would be described by modern morphologists as lower, not upper,
sepals, etc. Darwin was aware that he used these terms incorrectly.) and
upper petal run to the wrong bundles on the column. I have seen no such
case.
This case apparently shows that not the least reliance can be placed on the
course of ducts. I am sure of my facts.
There is great adhesion and extreme displacement of parts where the organs
spring from the top of the ovarium. Asa Gray says ducts are very early
developed, and it seems to me wonderful that they should pursue this
course. It may be said that the lateral ducts in the labellum running into
the antero-lateral ovarian bundle is no argument that the labellum consists
of three organs blended together.
In desperation (and from the curious way the base of upper petals are
soldered at basal edges) I fancied the real form of upper sepal, upper
petal and lower sepal might be as represented by red lines, and that there
had been an incredible amount of splitting of sepals and petals and
subsequent fusion.
This seems a monstrous notion, but I have just looked at Bauer's drawing of
allied Bonatea, and there is a degree of lobing of petals and sepals which
would account for anything.
Now could you spare me a dry flower out of your Herbarium of Bonatea
speciosa (605/5. See "Fertilisation of Orchids," Edition I., page 304
(note), where the resemblances between the anomalous vessels of Bonatea and
Habenaria are described. On November 14th, 1861, he wrote to Sir Joseph:
"You are a true friend in need. I can hardly bear to let the Bonatea soak
long enough."), that I might soak and look for ducts. If I cannot explain
the case of Habenaria all my work is smashed. I was a fool ever to touch
orchids.
LETTER 606. TO J.D. HOOKER.
Down, November 17th [1861].
What two very interesting and useful letters you have sent me. You rather
astound me with respect to value of grounds of generalisation in the
morphology of plants. It reminds me that years ago I sent you a grass to
name, and your answer was, "It is certainly Festuca (so-and-so), but it
agrees as badly with the description as most plants do." I have often
laughed over this answer of a great botanist...Lindley, from whom I asked
for an orchid with a simple labellum, has most kindly sent me a lot of what
he marks "rare" and "rarissima" of peloric orchids, etc., but as they are
dried I know not whether they will be of use. He has been most kind, and
has suggested my writing to Lady D. Nevill, who has responded in a
wonderfully kind manner, and has sent a lot of treasures. But I must stop;
otherwise, by Jove, I shall be transformed into a botanist. I wish I had
been one; this morphology is surprisingly interesting. Looking to your
note, I may add that certainly the fifteen alternating bundles of spiral
vessels (mingled with odd beadlike vessels in some cases) are present in
many orchids. The inner whorl of anther ducts are oftenest aborted. I
must keep clear of Apostasia, though I have cast many a longing look at it
in Bauer. (606/1. Apostasia has two fertile anthers like Cypripedium. It
is placed by Engler and Prantl in the Apostasieae or Apostasiinae, among
the Orchideae, by others in a distinct but closely allied group.)
I hope I may be well enough to read my own paper on Thursday, but I have
been very seedy lately. (606/2. "On the two Forms, or Dimorphic
Condition, in the Species of the Genus Primula," "Linn. Soc. Journ." 1862.
He did read the paper, but it cost him the next day in bed. "Life and
Letters," III., page 299.) I see there is a paper at the Royal on the same
night, which will more concern you, on fossil plants of Bovey (606/3.
Oswald Heer, "The Fossil Flora of Bovey Tracey," "Phil. Trans. R. Soc."
1862, page 1039.), so that I suppose I shall not have you; but you must
read my paper when published, as I shall very much like to hear what you
think. It seems to me a large field for experiment. I shall make use of
my Orchid little volume in illustrating modification of species doctrine,
but I keep very, very doubtful whether I am not doing a foolish action in
publishing. How I wish you would keep to your old intention and write a
book on plants. (606/4. Possibly a book similar to that described in
Letter 696.)
LETTER 607. TO G. BENTHAM.
Down, November 26th [1861].
Our notes have crossed on the road. I know it is an honour to have a paper
in the "Transactions," and I am much obliged to you for proposing it, but I
should greatly prefer to publish in the "Journal." Nor does this apply
exclusively to myself, for in old days at the Geological Society I always
protested against an abstract appearing when the paper itself might appear.
I abominate also the waste of time (and it would take me a day) in making
an abstract. If the referee on my paper should recommend it to appear in
the "Transactions," will you be so kind as to lay my earnest request before
the Council that it may be permitted to appear in the "Journal?"
You must be very busy with your change of residence; but when you are
settled and have some leisure, perhaps you will be so kind as to give me
some cases of dimorphism, like that of Primula. Should you object to my
adding them to those given me by A. Gray? By the way, I heard from A. Gray
this morning, and he gives me two very curious cases in Boragineae.
LETTER 608. TO JOHN LINDLEY.
(608/1. In the following fragment occurs the earliest mention of Darwin's
work on the three sexual forms of Catasetum tridentatum. Sir R. Schomburgk
(608/2. "Trans. Linn. Soc." XVII., page 522.) described Catasetum
tridentatum, Monacanthus viridis and Myanthus barbatus occurring on a
single plant, but it remained for Darwin to make out that they are the
male, female and hermaphrodite forms of a single species. (608/3.
"Fertilisation of Orchids," Edition I., page 236; Edition II., page 196.)
With regard to the species of Acropera (Gongora) (608/4. Acropera
Loddigesii = Gongora galeata: A. luteola = G. fusca ("Index Kewensis").)
he was wrong in his surmise. The apparent sterility seems to be explicable
by Hildebrand's discovery (608/5. "Bot. Zeitung," 1863 and 1865.) that in
some orchids the ovules are not developed until pollinisation has occurred.
(608/6. "Fertilisation of Orchids," Edition II., page 172. See Letter
633.))
Down, December 15th [1861].
I am so nearly ready for press that I will not ask for anything more;
unless, indeed, you stumbled on Mormodes in flower. As I am writing I will
just mention that I am convinced from the rudimentary state of the ovules,
and from the state of the stigma, that the whole plant of Acropera luteola
(and I believe A. Loddigesii) is male. Have you ever seen any form from
the same countries which could be the females? Of course no answer is
expected unless you have ever observed anything to bear on this. I may add
[judging from the] state of the ovules and of the pollen [that]:--
Catasetum tridentatum is male (and never seeds, according to Schomburgk,
whom you have accidentally misquoted in the "Vegetable Kingdom").
Monacanthus viridis is female. Myanthus barbatus is the hermaphrodite form
of same species.
LETTER 609. TO J.D. HOOKER.
Down, December 18th [1861].
Thanks for your note. I have not written for a long time, for I always
fancy, busy as you are, that my letters must be a bore; though I like
writing, and always enjoy your notes. I can sympathise with you about fear
of scarlet fever: to the day of my death I shall never forget all the
sickening fear about the other children, after our poor little baby died of
it. The "Genera Plantarum" must be a tremendous work, and no doubt very
valuable (such a book, odd as it may appear, would be very useful even to
me), but I cannot help being rather sorry at the length of time it must
take, because I cannot enter on and understand your work. Will you not be
puzzled when you come to the orchids? It seems to me orchids alone would
be work for a man's lifetime; I cannot somehow feel satisfied with
Lindley's classification; the Malaxeae and Epidendreae seem to me very
artificially separated. (609/1. Pfitzer (in the "Pflanzenfamilien")
places Epidendrum in the Laeliinae-Cattleyeae, Malaxis in the Liparidinae.
He states that Bentham united the Malaxideae and Epidendreae.) Not that I
have seen enough to form an opinion worth anything.
Your African plant seems to be a vegetable Ornithorhynchus, and indeed much
more than that. (609/2. See Sir J.D. Hooker, "On Welwitschia, a new genus
of Gnetaceae." "Linn. Soc. Trans." XXIV., 1862-3.) The more I read about
plants the more I get to feel that all phanerogams seem comparable with one
class, as lepidoptera, rather than with one kingdom, as the whole insecta.
(609/3. He wrote to Hooker (December 28th, 1861): "I wrote carelessly
about the value of phanerogams; what I was thinking of was that the sub-
groups seemed to blend so much more one into another than with most classes
of animals. I suspect crustacea would show more difference in the extreme
forms than phanerogams, but, as you say, it is wild speculation. Yet it is
very strange what difficulty botanists seem to find in grouping the
families together into masses.")
Thanks for your comforting sentence about the accursed ducts (accursed
though they be, I should like nothing better than to work at them in the
allied orders, if I had time). I shall be ready for press in three or four
weeks, and have got all my woodcuts drawn. I fear much that publishing
separately will prove a foolish job, but I do not care much, and the work
has greatly amused me. The Catasetum has not flowered yet!
In writing to Lindley about an orchid which he sent me, I told him a little
about Acropera, and in answer he suggests that Gongora may be its female.
He seems dreadfully busy, and I feel that I have more right to kill you
than to kill him; so can you send me one or at most two dried flowers of
Gongora? if you know the habitat of Acropera luteola, a Gongora from the
same country would be the best, but any true Gongora would do; if its
pollen should prove as rudimentary as that of Monacanthus relatively to
Catasetum, I think I could easily perceive it even in dried specimens when
well soaked.
I have picked a little out of Lecoq, but it is awful tedious hunting.
Bates is getting on with his natural history travels in one volume.
(609/4. H.W. Bates, the "Naturalist on the Amazons," 1863. See Volume I.,
Letters 123, 148, also "Life and Letters," Volume II., page 381.) I have
read the first chapter in MS., and I think it will be an excellent book and
very well written; he argues, in a good and new way to me, that tropical
climate has very little direct relation to the gorgeous colouring of
insects (though of course he admits the tropics have a far greater number
of beautiful insects) by taking all the few genera common to Britain and
Amazonia, and he finds that the species proper to the latter are not at all
more beautiful. I wonder how this is in species of the same restricted
genera of plants.
If you can remember it, thank Bentham for getting my Primula paper printed
so quickly. I do enjoy getting a subject off one's hands completely.
I have now got dimorphism in structure in eight natural orders just like
Primula. Asa Gray sent me dried flowers of a capital case in Amsinkia
spectabilis, one of the Boragineae. I suppose you do not chance to have
the plant alive at Kew.
LETTER 610. TO A.G. MORE.
Down, June 7th, 1862.
If you are well and have leisure, will you kindly give me one bit of
information: Does Ophrys arachnites occur in the Isle of Wight? or do the
intermediate forms, which are said to connect abroad this species and the
bee-orchis, ever there occur?
Some facts have led me to suspect that it might just be possible, though
improbable in the highest degree, that the bee [orchis] might be the
self-fertilising form of O. arachnites, which requires insects' aid,
something [in the same way] as we have self-fertilising flowers of the
violet and others requiring insects. I know the case is widely different,
as the bee is borne on a separate plant and is incomparably commoner. This
would remove the great anomaly of the bee being a perpetual self-
fertiliser. Certain Malpighiaceae for years produce only one of the two
forms. What has set my head going on this is receiving to-day a bee having
one alone of the best marked characters of O. arachnites. (610/1. Ophrys
arachnites is probably more nearly allied to O. aranifera than to O.
apifera. For a case somewhat analogous to that suggested see the
description of O. scolopax in "Fertilisation of Orchids," Edition II., page
52.) Pray forgive me troubling you.
LETTER 611. TO G. BENTHAM.
Down, June 22nd [1862?].
Here is a piece of presumption! I must think that you are mistaken in
ranking Hab[enaria] chlorantha (611/1. In Hooker's "Students' Flora,"
1884, page 395, H. chlorantha is given as a subspecies of H. bifolia. Sir
J.D. Hooker adds that they are "according to Darwin, distinct, and require
different species of moths to fertilise them. They vary in the position
and distances of their anther-cells, but intermediates occur." See
"Fertilisation of Orchids," Edition II., page 73.) as a variety of H.
bifolia; the pollen-masses and stigma differ more than in most of the best
species of Orchis. When I first examined them I remember telling Hooker
that moths would, I felt sure, fertilise them in a different manner; and I
have just had proof of this in a moth sent me with the pollinia (which can
be easily recognised) of H. chlorantha attached to its proboscis, instead
of to the sides of its face, as an H. bifolia.
Forgive me scribbling this way; but when a man gets on his hobby-horse he
always is run away with. Anyhow, nothing here requires any answer.
LETTER 612. TO J.D. HOOKER.
Down, [September] 14th [1862].
Your letter is a mine of wealth, but first I must scold you: I cannot
abide to hear you abuse yourself, even in joke, and call yourself a stupid
dog. You, in fact, thus abuse me, because for long years I have looked up
to you as the man whose opinion I have valued more on any scientific
subject than any one else in the world. I continually marvel at what you
know, and at what you do. I have been looking at the "Genera" (612/1.
"Genera Plantarum," by Bentham and Hooker, Volume I., Part I., 1862.), and
of course cannot judge at all of its real value, but I can judge of the
amount of condensed facts under each family and genus.
I am glad you know my feeling of not being able to judge about one's own
work; but I suspect that you have been overworking. I should think you
could not give too much time to Wellwitchia (I spell it different every
time I write it) (612/2. "On Welwitschia," "Linn. Soc. Trans." [1862],
XXIV., 1863.); at least I am sure in the animal kingdom monographs cannot
be too long on the osculant groups.
Hereafter I shall be excessively glad to read a paper about Aldrovanda
(612/3. See "Insectivorous Plants," page 321.), and am very much obliged
for reference. It is pretty to see how the caught flies support Drosera;
nothing else can live.
Thanks about plants with two kinds of anthers. I presume (if an included
flower was a Cassia) (612/4. Todd has described a species of Cassia with
an arrangement of stamens like the Melastomads. See Chapter 2.X.II.) that
Cassia is like lupines, but with some stamens still more rudimentary. If I
hear I will return the three Melastomads; I do not want them, and, indeed,
have cuttings. I am very low about them, and have wasted enormous labour
over them, and cannot yet get a glimpse of the meaning of the parts. I
wish I knew any botanical collector to whom I could apply for seeds in
their native land of any Heterocentron or Monochoetum; I have raised plenty
of seedlings from your plants, but I find in other cases that from a
homomorphic union one generally gets solely the parent form. Do you chance
to know of any botanical collector in Mexico or Peru? I must not now
indulge myself with looking after vessels and homologies. Some future time
I will indulge myself. By the way, some time I want to talk over the
alternation of organs in flowers with you, for I think I must have quite
misunderstood you that it was not explicable.
I found out the Verbascum case by pure accident, having transplanted one
for experiment, and finding it to my astonishment utterly sterile. I
formerly thought with you about rarity of natural hybrids, but I am
beginning to change: viz., oxlips (not quite proven), Verbascum, Cistus
(not quite proven), Aegilops triticoides (beautifully shown by Godron),
Weddell's and your orchids (612/5. For Verbascum see "Animals and Plants,"
Edition II., Volume I., page 356; for Cistus, Ibid., Edition II., Volume
I., page 356, Volume II., page 122; for Aegilops, Ibid., Edition II.,
Volume I., page 330, note.), and I daresay many others recorded. Your
letters are one of my greatest pleasures in life, but I earnestly beg you
never to write unless you feel somewhat inclined, for I know how hard you
work, as I work only in the morning it is different with me, and is only a
pleasant relaxation. You will never know how much I owe to you for your
constant kindness and encouragement.
LETTER 613. TO JOHN LUBBOCK (Lord Avebury).
Cliff Cottage, Bournemouth, Hants, September 2nd [1862].
Hearty thanks for your note. I am so glad that your tour answered so
splendidly. My poor patients (613/1. Mrs. Darwin and one of her sons,
both recovering from scarlet fever.) got here yesterday, and are doing
well, and we have a second house for the well ones. I write now in great
haste to beg you to look (though I know how busy you are, but I cannot
think of any other naturalist who would be careful) at any field of common
red clover (if such a field is near you) and watch the hive-bees: probably
(if not too late) you will see some sucking at the mouth of the little
flowers and some few sucking at the base of the flowers, at holes bitten
through the corollas. All that you will see is that the bees put their
heads deep into the [flower] head and rout about. Now, if you see this, do
for Heaven's sake catch me some of each and put in spirits and keep them
separate. I am almost certain that they belong to two castes, with long
and short proboscids. This is so curious a point that it seems worth
making out. I cannot hear of a clover field near here.
LETTER 614. TO JOHN LUBBOCK (Lord Avebury).
Cliff Cottage, Bournemouth, Wednesday, September 3rd [1862].
I beg a million pardons. Abuse me to any degree, but forgive me: it is
all an illusion (but almost excusable) about the bees. (614/1. H. Muller,
"Fertilisation of Flowers," page 186, describes hive-bees visiting
Trifolium pratense for the sake of the pollen. Darwin may perhaps have
supposed that these were the variety of bees whose proboscis was long
enough to reach the nectar. In "Cross and Self Fertilisation," page 361,
Darwin describes hive-bees apparently searching for a secretion on the
calyx. In the same passage in "Cross and Self Fertilisation" he quotes
Muller as stating that hive-bees obtain nectar from red clover by breaking
apart the petals. This seems to us a misinterpretation of the "Befruchtung
der Blumen," page 224.) I do so hope that you have not wasted any time
from my stupid blunder. I hate myself, I hate clover, and I hate bees.
(FIGURE 10.--DIAGRAM OF CRUCIFEROUS FLOWER.
FIGURE 11.--DISSECTION OF CRUCIFEROUS FLOWER.
Laid flat open, showing by dotted lines the course of spiral vessels in all
the organs; sepals and petals shown on one side alone, with the stamens on
one side above with course of vessels indicated, but not prolonged. Near
side of pistil with one spiral vessel cut away.)
LETTER 615. TO J.D. HOOKER.
Cliff Cottage, Bournemouth, September 11th, 1862.
You once told me that Cruciferous flowers were anomalous in alternation of
parts, and had given rise to some theory of dedoublement.
Having nothing on earth to do here, I have dissected all the spiral vessels
in a flower, and instead of burning my diagrams [Figures 10 and 11], I send
them to you, you miserable man. But mind, I do not want you to send me a
discussion, but just some time to say whether my notions are rubbish, and
then burn the diagrams. It seems to me that all parts alternate
beautifully by fours, on the hypothesis that two short stamens of outer
whorl are aborted (615/1. The view given by Darwin is (according to
Eichler) that previously held by Knuth, Wydler, Chatin, and others.
Eichler himself believes that the flower is dimerous, the four longer
stamens being produced by the doubling or splitting of the upper (i.e.
antero-posterior) pair of stamens. If this view is correct, and there are
good reasons for it, it throws much suspicion on the evidence afforded by
the course of vessels, for there is no trace of the common origin of the
longer stamens in the diagram (Figure 11). Again, if Eichler is right, the
four vessels shown in the section of the ovary are misleading. Darwin
afterwards gave a doubtful explanation of this, and concluded that the
ovary is dimerous. See Letter 616.); and this view is perhaps supported by
their being so few, only two sub-bundles in the two lateral main bundles,
where I imagine two short stamens have aborted, but I suppose there is some
valid objection against this notion. The course of the side vessels in the
sepals is curious, just like my difficulty in Habenaria. (615/2. See
Letter 605.) I am surprised at the four vessels in the ovarium. Can this
indicate four confluent pistils? anyhow, they are in the right alternating
position. The nectary within the base of the shorter stamens seems to
cause the end sepals apparently, but not really, to arise beneath the
lateral sepals.
I think you will understand my diagrams in five minutes, so forgive me for
bothering you. My writing this to you reminds me of a letter which I
received yesterday from Claparede, who helped the French translatress of
the "Origin" (615/3. The late Mlle. Royer.), and he tells me he had
difficulty in preventing her (who never looked at a bee's cell) from
altering my whole description, because she affirmed that an hexagonal prism
must have an hexagonal base! Almost everywhere in the "Origin," when I
express great doubt, she appends a note explaining the difficulty, or
saying that there is none whatever!! (615/4. See "Life and Letters," II.,
page 387.) It is really curious to know what conceited people there are in
the world (people, for instance, after looking at one Cruciferous flower,
explain their homologies).
This is a nice, but most barren country, and I can find nothing to look at.
Even the brooks and ponds produce nothing. The country is like Patagonia.
my wife is almost well, thank God, and Leonard is wonderfully improved
...Good God, what an illness scarlet fever is! The doctor feared rheumatic
fever for my wife, but she does not know her risk. It is now all over.
(FIGURE 12.)
LETTER 616. TO J.D. HOOKER.
Cliff Cottage, Bournemouth, Thursday Evening [September 18th, 1862].
Thanks for your pleasant note, which told me much news, and upon the whole
good, of yourselves. You will be awfully busy for a time, but I write now
to say that if you think it really worth while to send me a few Dielytra,
or other Fumariaceous plant (which I have already tried in vain to find
here) in a little tin box, I will try and trace the vessels; but please
observe, I do not know that I shall have time, for I have just become
wonderfully interested in experimenting on Drosera with poisons, etc. If
you send any Fumariaceous plant, send if you can, also two or three single
balsams. After writing to you, I looked at vessels of ovary of a
sweet-pea, and from this and other cases I believe that in the ovary the
midrib vessel alone gives homologies, and that the vessels on the edge of
the carpel leaf often run into the wrong bundle, just like those on the
sides of the sepals. Hence I [suppose] in Crucifers that the ovarium
consists of two pistils; AA [Figure 12] being the midrib vessels, and BB
being those formed of the vessels on edges of the two carpels, run
together, and going to wrong bundles. I came to this conclusion before
receiving your letter.
I wonder why Asa Gray will not believe in the quaternary arrangement; I had
fancied that you saw some great difficulty in the case, and that made me
think that my notion must be wrong.
LETTER 617. TO J.D. HOOKER.
Down, September 27th [1862].
Masdevallia turns out nothing wonderful (617/1. This may refer to the
homologies of the parts. He was unable to understand the mechanism of the
flower.--"Fertilisation of Orchids," Edition II., page 136.); I was merely
stupid about it; I am not the less obliged for its loan, for if I had lived
till 100 years old I should have been uneasy about it. It shall be
returned the first day I send to Bromley. I have steamed the other plants,
and made the sensitive plant very sensitive, and shall soon try some
experiments on it. But after all it will only be amusement. Nevertheless,
if not causing too much trouble, I should be very glad of a few young
plants of this and Hedysarum in summer (617/2. Hedysarum or Desmodium
gyrans, the telegraph-plant.), for this kind of work takes no time and
amuses me much. Have you seeds of Oxalis sensitiva, which I see mentioned
in books? By the way, what a fault it is in Henslow's "Botany" that he
gives hardly any references; he alludes to great series of experiments on
absorption of poison by roots, but where to find them I cannot guess.
Possibly the all-knowing Oliver may know. I can plainly see that the
glands of Drosera, from rapid power (almost instantaneous) of absorption
and power of movement, give enormous advantage for such experiments. And
some day I will enjoy myself with a good set to work; but it will be a
great advantage if I can get some preliminary notion on other sensitive
plants and on roots.
Oliver said he would speak about some seeds of Lythrum hyssopifolium being
preserved for me. By the way, I am rather disgusted to find I cannot
publish this year on Lythrum salicaria; I must make 126 additional crosses.
All that I expected is true, but I have plain indication of much higher
complexity. There are three pistils of different structure and functional
power, and I strongly suspect altogether five kinds of pollen all
different in this one species! (617/3. See "Forms of Flowers," Edition
II., page 138.)
By any chance have you at Kew any odd varieties of the common potato? I
want to grow a few plants of every variety, to compare flowers, leaves,
fruit, etc., as I have done with peas, etc. (617/4. "Animals and Plants,"
Edition II., Volume I., page 346. Compare also the similar facts with
regard to cabbages, loc. cit., page 342. Some of the original specimens
are in the Botanical Museum at Cambridge.)
LETTER 618. J.D. HOOKER TO CHARLES DARWIN.
(618/1. The following is part of Letter 144, Volume I. It refers to
reviews of "Fertilisation of Orchids" in the "Gardeners' Chronicle," 1862,
pages 789, 863, 910, and in the "Natural History Review," October, 1862,
page 371.)
November 7th, 1862.
Dear old Darwin,
I assure you it was not my fault! I worried Lindley over and over again to
notice your orchid book in the "Chronicle" by the very broadest hints man
could give. (618/2. See "Life and Letters," III., page 273.) At last he
said, "really I cannot, you must do it for me," and so I did--volontiers.
Lindley felt that he ought to have done it himself, and my main effort was
to write it "a la Lindley," and in this alone I have succeeded--that people
all think it is exactly Lindley's style!!! which diverts me vastly. The
fact is, between ourselves, I fear that poor L. is breaking up--he said
that he could not fix his mind on your book. He works himself beyond his
mental or physical powers.
And now, my dear Darwin, I may as well make a clean breast of it, and tell
you that I wrote the "Nat. Hist. Review" notice too--to me a very difficult
task, and one I fancied I failed in, comparatively. Of this you are no
judge, and can be none; you told me to tell Oliver it pleased you, and so I
am content and happy.
LETTER 619. TO W.E. DARWIN.
Down, 4th [about 1862-3?]
I have been looking at the fertilisation of wheat, and I think possibly you
might find something curious. I observed in almost every one of the
pollen-grains, which had become empty and adhered to (I suppose the viscid)
branching hairs of the stigma, that the pollen-tube was always (?) emitted
on opposite side of grain to that in contact with the branch of the stigma.
This seems very odd. The branches of the stigma are very thin, formed
apparently of three rows of cells of hardly greater diameter than pollen-
tube. I am astonished that the tubes should be able to penetrate the
walls. The specimens examined (not carefully by me) had pollen only during
few hours on stigma; and the mere SUSPICION has crossed me that the pollen-
tubes crawl down these branches to the base and then penetrate the
stigmatic tissue. (619/1. See Strasburger's "Neue Untersuchungen uber den
Befruchtungsvorgang bei den Phanerogamen," 1884. In Alopecurus pratensis
he describes the pollen as adhering to the end of a projection from the
stigma where it germinates; the tube crawls along or spirally round this
projection until it reaches the angle where the stigmatic branch is given
off; here it makes an entrance and travels in the middle lamella between
two cells.) The paleae open for a short period for stigma to be dusted,
and then close again, and such travelling down would take place under
protection. High powers and good adjustment are necessary. Ears expel
anthers when kept in water in room; but the paleae apparently do not open
and expose stigma; but the stigma could easily be artificially impregnated.
If I were you I would keep memoranda of points worth attending to.
2.X.II. MELASTOMACEAE, 1862-1881.
(620/1. The following series of letters (620-630) refers to the
Melastomaceae and certain other flowers of analogous form. In 1862 Darwin
attempted to explain the existence of two very different sets of stamens in
these plants as a case of dimorphism, somewhat analogous to the state of
things in Primula. In this view he was probably wrong, but this does not
diminish the interest of the crossing experiments described in the letters.
The persistence of his interest in this part of the subject is shown in the
following passage from his Preface to the English translation of H.
Muller's "Befruchtung der Blumen"; the passage is dated February, 1882, but
was not published until the following year.
"There exist also some few plants the flowers of which include two sets of
stamens, differing in the shape of the anthers and in the colour of the
pollen; and at present no one knows whether this difference has any
functional significance, and this is a point which ought to be determined."
It is not obvious why he spoke of the problem as if no light had been
thrown on it, since in 1881 Fritz Muller had privately (see Letter 629)
offered an explanation which Darwin was strongly inclined to accept.
(620/2. H. Muller published ("Nature," August 4th, 1881) a letter from his
brother Fritz giving the theory in question for Heeria. Todd ("American
Naturalist," April 1882), described a similar state of things in Solanum
rostratum and in Cassia: and H.O. Forbes ("Nature," August 1882, page 386)
has done the same for Melastoma. In Rhexia virginica Mr. W.H. Leggett
("Bulletin Torrey Bot. Club, New York," VIII., 1881, page 102) describes
the curious structure of the anther, which consists of two inflated
portions and a tubular part connecting the two. By pressing with a blunt
instrument on one of the ends, the pollen is forced out in a jet through a
fine pore in the other inflated end. Mr. Leggett has seen bees treading on
the anthers, but could not get near enough to see the pollen expelled. In
the same journal, Volume IX., page 11, Mr. Bailey describes how in
Heterocentron roseum, "upon pressing the bellows-like anther with a blunt
pencil, the pollen was ejected to a full inch in distance." On
Lagerstroemia as comparable with the Melastomads see Letter 689.) Fritz
Muller's theory with regard to the Melastomads and a number of analogous
cases in other genera are discussed in H. Muller's article in "Kosmos"
(620/3. "Kosmos," XIII., 1883, page 241.), where the literature is given.
F. Muller's theory is that in Heeria the yellow anthers serve merely as a
means of attracting pollen-collecting bees, while the longer stamens with
purple or crimson anthers supply pollen for fertilising purposes. If
Muller is right the pollen from the yellow anthers would not normally reach
the stigma. The increased vigour observed in the seedlings from the yellow
anthers would seem to resemble the good effect of a cross between different
individuals of the same species as worked out in "Cross and Self
Fertilisation," for it is difficult to believe that the pollen of the
purple anthers has become, by adaptation, less effective than that of the
yellow anthers. In the letters here given there is some contradiction
between the statements as to the position of the two sets of stamens in
relation to the sepals. According to Eichler ("Bluthendiagramme, II., page
482) the longer stamens may be either epipetalous or episepalous in this
family.
The work on the Melastomads is of such intrinsic importance that we have
thought it right to give the correspondence in considerable detail; we have
done so in spite of the fact that Darwin arrived at no definite conclusion,
and in spite of an element of confusion and unsatisfactoriness in the
series of letters. This applies also to Letter 629, written after Darwin
had learned Fritz Muller's theory, which is obscured by some errors or
slips of the pen.)
LETTER 620. TO G. BENTHAM.
Down, February 3rd [1862?]
As you so kindly helped me before on dimorphism, will you forgive me
begging for a little further information, if in your power to give it? The
case is that of the Melastomads with eight stamens, on which I have been
experimenting. I am perplexed by opposed statements: Lindley says the
stamens which face the petals are sterile; Wallich says in Oxyspora
paniculata that the stamens which face the sepals are destitute of pollen;
I find plenty of apparently good pollen in both sets of stamens in
Heterocentron [Heeria], Monochoetum, and Centradenia. Can you throw any
light on this? But there is another point on which I am more anxious for
information. Please look at the enclosed miserable diagram. I find that
the pollen of the yellow petal-facing stamens produce more than twice as
much seed as the pollen of the purple sepal-facing stamens. This is
exactly opposed to Lindley's statement--viz., that the petal-facing stamens
are sterile. But I cannot at present believe that the case has any
relation to abortion; it is hardly possible to believe that the longer and
very curious stamens, which face the sepals in this Heterocentron, are
tending to be rudimentary, though their pollen applied to their own flowers
produces so much less seed. It is conformable with what we see in Primula
that the [purple] sepal-facing anthers, which in the plant seen by me stood
quite close on each side of the stigma, should have been rendered less
fitted to fertilise the stigma than the stamens on the opposite side of the
flower. Hence the suspicion has crossed me that if many plants of the
Heterocentron roseum were examined, half would be found with the pistil
nearly upright, instead of being rectangularly bent down, as shown in the
diagram (620/4. According to Willis, "Flowering Plants and Ferns," 1897,
Volume II., page 252, the style in Monochoetum, "at first bent downwards,
moves slowly up till horizontal."); or, if the position of pistil is fixed,
that in half the plants the petal-facing stamens would bend down, and in
the other half of the plants the sepal-facing stamens would bend down as in
the diagram. I suspect the former case, as in Centradenia I find the
pistil nearly straight. Can you tell me? (620/5. No reply by Mr. Bentham
to this or the following queries has been found.) Can the name
Heterocentron have any reference to such diversity? Would it be asking too
great a favour to ask you to look at dried specimens of Heterocentron
roseum (which would be best), or of Monochoetum, or any eight-stamened
Melastomad, of which you have specimens from several localities (as this
would ensure specimens having been taken from distinct plants), and observe
whether the pistil bends differently or stamens differently in different
plants? You will at once see that, if such were the fact, it would be a
new form of dimorphism, and would open up a large field of inquiry with
respect to the potency of the pollen in all plants which have two sets of
stamens--viz., longer and shorter. Can you forgive me for troubling you at
such unreasonable length? But it is such waste of time to experiment
without some guiding light. I do not know whether you have attended
particularly to Melastoma; if you have not, perhaps Hooker or Oliver may
have done so. I should be very grateful for any information, as it will
guide future experiments.
P.S.--Do you happen to know, when there are only four stamens, whether it
is the petal or sepal-facers which are preserved? and whether in the four-
stamened forms the pistil is rectangularly bent or is straight?
LETTER 621. TO ASA GRAY.
Down, February 16th [1862?].
I have been trying a few experiments on Melastomads; and they seem to
indicate that the pollen of the two curious sets of anthers (i.e. the
petal-facers and the sepal-facers) have very different powers; and it does
not seem that the difference is connected with any tendency to abortion in
the one set. Now I think I can understand the structure of the flower and
means of fertilisation, if there be two forms,--one with the pistil bent
rectangularly out of the flower, and the other with it nearly straight.
Our hot-house and green-house plants have probably all descended by
cuttings from a single plant of each species; so I can make out nothing
from them. I applied in vain to Bentham and Hooker; but Oliver picked out
some sentences from Naudin, which seem to indicate differences in the
position of the pistil.
I see that Rhexia grows in Massachusetts; and I suppose has two different
sets of stamens. Now, if in your power, would you observe the position of
the pistil in different plants, in lately opened flowers of the same age?
(I specify this because in Monochaetum I find great changes of position in
the pistils and stamens, as flower gets old). Supposing that my prophecy
should turn out right, please observe whether in both forms the passage
into the flower is not [on] the upper side of the pistil, owing to the
basal part of the pistil lying close to the ring of filaments on the under
side of the flower. Also I should like to know the colour of the two sets
of anthers. This would take you only a few minutes, and is the only way I
see that I can find out whether these plants are dimorphic in this peculiar
way--i.e., only in the position of the pistil (621/1. In Exacum and in
Saintpaulia the flowers are dimorphic in this sense: the style projects to
either the right or the left side of the corolla, from which it follows
that a right-handed flower would fertilise a left-handed one, and vice
versa. See Willis, "Flowering Plants and Ferns," 1897, Volume I., page
73.) and in its relation to the two kinds of pollen. I am anxious about
this, because if it should prove so, it will show that all plants with
longer and shorter or otherwise different anthers will have to be examined
for dimorphism.
LETTER 622. TO ASA GRAY.
March 15th [1862].
...I wrote some little time ago about Rhexia; since then I have been
carefully watching and experimenting on another genus, Monochaetum; and I
find that the pistil is first bent rectangularly (as in the sketch sent),
and then in a few days becomes straight: the stamens also move. If there
be not two forms of Rhexia, will you compare the position of the part in
young and old flowers? I have a suspicion (perhaps it will be proved wrong
when the seed-capsules are ripe) that one set of anthers are adapted to the
pistil in early state, and the other set for it in its later state. If
bees visit the Rhexia, for Heaven's sake watch exactly how the anther and
stigma strike them, both in old and young flowers, and give me a sketch.
Again I say, do not hate me.
LETTER 623. TO J.D. HOOKER.
Leith Hill Place, Dorking, Thursday, 15th [May 1862].
You stated at the Linnean Society that different sets of seedling Cinchona
(623/1. Cinchona is apparently heterostyled: see "Forms of Flowers,"
Edition II., page 134.) grew at very different rate, and from my Primula
case you attributed it probably to two sorts of pollen. I confess I
thought you rash, but I now believe you were quite right. I find the
yellow and crimson anthers of the same flower in the Melastomatous
Heterocentron roseum have different powers; the yellow producing on the
same plant thrice as many seeds as the crimson anthers. I got my
neighbour's most skilful gardener to sow both kinds of seeds, and yesterday
he came to me and said it is a most extraordinary thing that though both
lots have been treated exactly alike, one lot all remain dwarfs and the
other lot are all rising high up. The dwarfs were produced by the pollen
of the crimson anthers. In Monochaetum ensiferum the facts are more
complex and still more strange; as the age and position of the pistils
comes into play, in relation to the two kinds of pollen. These facts seem
to me so curious that I do not scruple to ask you to see whether you can
lend me any Melastomad just before flowering, with a not very small flower,
and which will endure for a short time a greenhouse or sitting-room; when
fertilised and watered I could send it to Mr. Turnbull's to a cool stove to
mature seed. I fully believe the case is worth investigation.
P.S.--You will not have time at present to read my orchid book; I never
before felt half so doubtful about anything which I published. When you
read it, do not fear "punishing" me if I deserve it.
Adios. I am come here to rest, which I much want.
Whenever you have occasion to write, pray tell me whether you have
Rhododendron Boothii from Bhootan, with a smallish yellow flower, and
pistil bent the wrong way; if so, I would ask Oliver to look for nectary,
for it is an abominable error of Nature that must be corrected. I could
hardly believe my eyes when I saw the pistil.
LETTER 624. TO ASA GRAY.
January 19th [1863].
I have been at those confounded Melastomads again; throwing good money
(i.e. time) after bad. Do you remember telling me you could see no nectar
in your Rhexia? well, I can find none in Monochaetum, and Bates tells me
that the flowers are in the most marked manner neglected by bees and
lepidoptera in Amazonia. Now the curious projections or horns to the
stamens of Monochaetum are full of fluid, and the suspicion occurs to me
that diptera or small hymenoptera may puncture these horns like they
puncture (proved since my orchid book was published) the dry nectaries of
true Orchis. I forget whether Rhexia is common; but I very much wish you
would next summer watch on a warm day a group of flowers, and see whether
they are visited by small insects, and what they do.
LETTER 625. TO I.A. HENRY.
Down, January 20th [1863].
...You must kindly permit me to mention any point on which I want
information. If you are so inclined, I am curious to know from systematic
experiments whether Mr. D. Beaton's statement that the pollen of two
shortest anthers of scarlet Pelargonium produce dwarf plants (625/1. See
"Animals and Plants," Edition II., Volume II., page 150, for a brief
account of Darwin's experiments on this genus. Also loc. cit., page 338
(note), for a suggested experiment.), in comparison with plants produced
from the same mother-plant by the pollen of longer stamens from the same
flower. It would aid me much in some laborious experiments on Melastomads.
I confess I feel a little doubtful; at least, I feel pretty nearly sure
that I know the meaning of short stamens in most plants. This summer (for
another object) I crossed Queen of Scarlet Pelargonium with pollen of long
and short stamens of multiflora alba, and it so turns out that plants from
short stamens are the tallest; but I believe this to have been mere chance.
My few crosses in Pelargonium were made to get seed from the central
peloric or regular flower (I have got one from peloric flower by pollen of
peloric), and this leads me to suggest that it would be very interesting to
test fertility of peloric flowers in three ways,--own peloric pollen on
peloric stigma, common pollen on peloric stigma, peloric pollen on common
stigma of same species. My object is to discover whether with change of
structure of flower there is any change in fertility of pollen or of female
organs. This might also be tested by trying peloric and common pollen on
stigma of a distinct species, and conversely. I believe there is a peloric
and common variety of Tropaeolum, and a peloric or upright and common
variation of some species of Gloxinia, and the medial peloric flowers of
Pelargonium, and probably others unknown to me.
LETTER 626. TO I.A. HENRY.
Hartfield, May 2nd [1863].
In scarlet dwarf Pelargonium, you will find occasionally an additional and
abnormal stamen on opposite and lower side of flower. Now the pollen of
this one occasional short stamen, I think, very likely would produce dwarf
plants. If you experiment on Pelargonium I would suggest your looking out
for this single stamen.
I observed fluctuations in length of pistil in Phloxes, but thought it was
mere variability.
If you could raise a bed of seedling Phloxes of any species except P.
Drummondii, it would be highly desirable to see if two forms are presented,
and I should be very grateful for information and flowers for inspection.
I cannot remember, but I know that I had some reason to look after Phloxes.
(626/1. See "Forms of Flowers," Edition II., page 119, where the
conjecture is hazarded that Phlox subulata shows traces of a former
heterostyled condition.)
I do not know whether you have used microscopes much yet. It adds
immensely to interest of all such work as ours, and is indeed indispensable
for much work. Experience, however, has fully convinced me that the use of
the compound without the simple microscope is absolutely injurious to
progress of N[atural] History (excepting, of course, with Infusoria). I
have, as yet, found no exception to the rule, that when a man has told me
he works with the compound alone his work is valueless.
LETTER 627. TO ASA GRAY.
March 20th [1863].
I wrote to him [Dr. H. Cruger, of Trinidad] to ask him to observe what the
insects did in the flowers of Melastomaceae: he says not proper season
yet, but that on one species a small bee seemed busy about the horn-like
appendages to the anthers. It will be too good luck if my study of the
flowers in the greenhouse has led me to right interpretation of these
appendages.
LETTER 628. TO J.D. HOOKER.
Down, November 28th [1871].
If you had come here on Sunday I should have asked you whether you could
give me seed or seedlings of any Melastomad which would flower soon to
experiment on! I wrote also to J. Scott to ask if he could give me seed.
Several years ago I raised a lot of seedlings of a Melastomad greenhouse
bush (Monochaetus or some such name) (628/1. Monochaetum.) from stigmas
fertilised separately by the two kinds of pollen, and the seedlings
differed remarkably in size, and whilst young, in appearance; and I never
knew what to think of the case (so you must not use it), and have always
wished to try again, but they are troublesome beasts to fertilise.
On the other hand I could detect no difference in the product from the two
coloured anthers of Clarkia. (628/2. Clarkia has eight stamens divided
into two groups which differ in the colour of the anthers.) If you want to
know further particulars of my experiments on Monochaetum (?) and Clarkia,
I will hunt for my notes. You ask about difference in pollen in the same
species. All dimorphic and trimorphic plants present such difference in
function and in size. Lythrum and the trimorphic Oxalis are the most
wonderful cases. The pollen of the closed imperfect cleistogamic flowers
differ in the transparency of the integument, and I think in size. The
latter point I could ascertain from my notes. The pollen or female organs
must differ in almost every individual in some manner; otherwise the pollen
of varieties and even distinct individuals of same varieties would not be
so prepotent over the individual plant's own pollen. Here follows a case
of individual differences in function of pollen or ovules or both. Some
few individuals of Reseda odorata and R. lutea cannot be fertilised, or
only very rarely, by pollen of the same plant, but can by pollen of any
other individual. I chanced to have two plants of R. odorata in this
state; so I crossed them and raised five seedlings, all of which were self
sterile and all perfectly fertile with pollen of any other individual
mignonette. So I made a self sterile race! I do not know whether these
are the kinds of facts which you require.
Think whether you can help me to seed or better seedlings (not cuttings) of
any Melastomad.
LETTER 629. TO F. MULLER.
Down, March 20th, 1881.
I have received the seeds and your most interesting letter of February 7th.
The seeds shall be sown, and I shall like to see the plants sleeping; but I
doubt whether I shall make any more detailed observations on this subject,
as, now that I feel very old, I require the stimulus of some novelty to
make me work. This stimulus you have amply given me in your remarkable
view of the meaning of the two-coloured stamens in many flowers. I was so
much struck with this fact with Lythrum, that I began experimenting on some
Melastomaceae, which have two sets of extremely differently coloured
anthers. After reading your letter I turned to my notes (made 20 years
ago!) to see whether they would support or contradict your suggestion. I
cannot tell yet, but I have come across one very remarkable result, that
seedlings from the crimson anthers were not 11/20ths of the size of
seedlings from the yellow anthers of the same flowers. Fewer good seeds
were produced by the crimson pollen. I concluded that the shorter stamens
were aborting, and that the pollen was not good. (629/1. "Shorter stamens"
seems to be a slip of the pen for "longer,"--unless the observations were
made on some genus in which the structure is unusual.) The mature pollen
is incoherent, and must be [word illegible] against the visiting insect's
body. I remembered this, and I find it said in my EARLY notes that bees
would never visit the flowers for pollen. This made me afterwards write to
the late Dr. Cruger in the West Indies, and he observed for me the flowers,
and saw bees pressing the anthers with their mandibles from the base
upwards, and this forced a worm-like thread of pollen from the terminal
pore, and this pollen the bees collected with their hind legs. So that the
Melastomads are not opposed to your views.
I am now working on the habits of worms, and it tires me much to change my
subject; so I will lay on one side your letter and my notes, until I have a
week's leisure, and will then see whether my facts bear on your views. I
will then send a letter to "Nature" or to the Linn. Soc., with the extract
of your letter (and this ought to appear in any case), with my own
observations, if they appear worth publishing. The subject had gone out of
my mind, but I now remember thinking that the imperfect action of the
crimson stamens might throw light on hybridism. If this pollen is
developed, according to your view, for the sake of attracting insects, it
might act imperfectly, as well as if the stamens were becoming rudimentary.
(629/2. As far as it is possible to understand the earlier letters it
seems that the pollen of the shorter stamens, which are adapted for
attracting insects, is the most effective.) I do not know whether I have
made myself intelligible.
LETTER 630. TO W. THISELTON-DYER.
Down, March 21st [1881].
I have had a letter from Fritz Muller suggesting a novel and very curious
explanation of certain plants producing two sets of anthers of different
colour. This has set me on fire to renew the laborious experiments which I
made on this subject, now 20 years ago. Now, will you be so kind as to
turn in your much worked and much holding head, whether you can think of
any plants, especially annuals, producing 2 such sets of anthers. I
believe that this is the case with Clarkia elegans, and I have just written
to Thompson for seeds. The Lythraceae must be excluded, as these are
heterostyled.
I have got seeds from Dr. King of some Melastomaceae, and will write to
Veitch to see if I can get the Melastomaceous genera Monochaetum and
Heterocentron or some such name, on which I before experimented. Now, if
you can aid me, I know that you will; but if you cannot, do not write and
trouble yourself.
2.X.III. CORRESPONDENCE WITH JOHN SCOTT, 1862-1871.
"If he had leisure he would make a wonderful observer, to my judgment; I
have come across no one like him."--Letter to J.D. Hooker, May 29th [1863].
(631/1. The following group of letters to John Scott, of whom some account
is given elsewhere (Volume I., Letters 150 and 151, and Index.) deal
chiefly with experimental work in the fertilisation of flowers. In
addition to their scientific importance, several of the letters are of
special interest as illustrating the encouragement and friendly assistance
which Darwin gave to his correspondent.)
LETTER 631. JOHN SCOTT TO CHARLES DARWIN.
Edinburgh Botanic Gardens, November 11th, 1862.
I take the liberty of addressing you for the purpose of directing your
attention to an error in one of your ingenious explanations of the
structural adaptations of the Orchidaceae in your late work. This occurs
in the genus Acropera, two species of which you assume to be unisexual, and
so far as known represented by male individuals only. Theoretically you
have no doubt assigned good grounds for this view; nevertheless,
experimental observations that I am now making have already convinced me of
its fallacy. And I thus hurriedly, and as you may think prematurely, direct
your attention to it, before I have seen the final result of my own
experiment, that you might have the longer time for reconsidering the
structure of this genus for another edition of your interesting book, if
indeed it be not already called for. I am furthermore induced to
communicate the results of my yet imperfect experiments in the belief that
the actuating principle of your late work is the elicitation of truth, and
that you will gladly avail yourself of this even at the sacrifice of much
ingenious theoretical argumentation.
Since I have had an opportunity of perusing your work on orchid
fertilisation, my attention has been particularly directed to the curiously
constructed floral organs of Acropera. I unfortunately have as yet had
only a few flowers for experimental enquiry, otherwise my remarks might
have been clearer and more satisfactory. Such as they are, however, I
respectfully lay [them] before you, with a full assurance of their
veracity, and I sincerely trust that as such you will receive them.
Your observations seem to have been chiefly directed to the A. luteola,
mine to the A. Loddigesii, which, however, as you remark, is in a very
similar constructural condition with the former; having the same narrow
stigmatic chamber, abnormally developed placenta, etc. In regard to the
former point--contraction of stigmatic chamber--I may remark that it does
not appear to be absolutely necessary that the pollen-masses penetrate this
chamber for effecting fecundation. Thus a raceme was produced upon a plant
of A. Loddigesii in the Botanic Gardens here lately; upon this I left only
six flowers. These I attempted to fertilise, but with two only of the six
have I been successful: I succeeded in forcing a single pollen-mass into
the stigmatic chamber of one of the latter, but I failed to do this on the
other; however, by inserting a portion of a pedicel with a pollinium
attached, I caused the latter to adhere, with a gentle press, to the mouth
of the stigmatic chamber. Both of these, as I have already remarked, are
nevertheless fertilised; one of them I have cut off for examination, and
its condition I will presently describe; the other is still upon the plant,
and promises fair to attain maturity. In regard to the other four flowers,
I may remark that though similarly fertilised--part having pollinia
inserted, others merely attached--they all withered and dropped off without
the least swelling of the ovary. Can it be, then, that this is really an
[andro-monoecious] species?--part of the flowers male, others truly
hermaphrodite.
In making longitudinal sections of the fertilised ovary before mentioned, I
found the basal portion entirely destitute of ovules, their place being
substituted by transparent cellular ramification of the placentae. As I
traced the placentae upwards, the ovules appeared, becoming gradually more
abundant towards its apex. A transverse section near the apex of the
ovary, however, still exhibited a more than ordinary placental
development--i.e. [congenitally?] considered--each end giving off two
branches, which meet each other in the centre of the ovary, the ovules
being irregularly and sparingly disposed upon their surfaces.
In regard to the mere question of fertilisation, then, I am perfectly
satisfied, but there are other points which require further elucidation.
Among these I may particularly refer to the contracted stigmatic chamber,
and the slight viscidity of its disk. The latter, however, may be a
consequence of uncongenial conditions--as you do not mention particularly
its examination by any author in its natural habitat. If such be the case,
the contracted stigmatic chamber will offer no real difficulty, should the
viscous exudations be only sufficient to render the mouth adhesive. For,
as I have already shown, the pollen-tubes may be emitted in this condition,
and effect fecundation without being in actual contact with the stigmatic
surface, as occurs pretty regularly in the fertilisation of the Stapelias,
for example. But, indeed, your own discovery of the independent
germinative capabilities of the pollen-grains of certain Orchidaceae is
sufficiently illustrative of this.
I may also refer to the peculiar abnormal condition that many at least of
the ovaries present in a comparative examination of the placentae, and of
which I beg to suggest the following explanation, though it is as yet
founded on limited observations. In examining certain young ovaries of A.
Loddigesii, I found some of them filled with the transparent membranous
fringes of more or less distinctly cellular matter, which, from your
description of the ovaries of luteola, appears to differ simply in the
greater development in the former species. Again, in others I found small
mammillary bodies, which appeared to be true ovules, though I could not
perfectly satisfy myself as to the existence of the micropyle or nucleus.
I unfortunately neglected to apply any chemical test. The fact, however,
that in certain of the examined ovaries few or none of the latter bodies
occurred--the placenta alone being developed in an irregular membranous
form, taken in conjunction with the results of my experiments--before
alluded to--on their fertilisation, leads me to infer that two sexual
conditions are presented by the flowers of this plant. In short, that many
of the ovaries are now normally abortive, though Nature occasionally makes
futile efforts for their perfect development, in the production of ovuloid
bodies; these then I regard as the male flowers. The others that are still
capable of fertilisation, and likewise possessing male organs, are
hermaphrodite, and must, I think, from the results of your comparative
examinations, present a somewhat different condition; as it can scarcely be
supposed that ovules in the condition you describe could ever be
fertilised.
This is at least the most plausible explanation I can offer for the
different results in my experiments on the fertilisation of apparently
similar morphologically constructed flowers; others may, however, occur to
you. Here there is not, as in the Catasetum, any external change visible
in the respective unisexual and bisexual flowers. And yet it would appear
from your researches that the ovules of Acropera are in a more highly
atrophied condition than occurs in Catasetum, though, as you likewise
remark, M. Neumann has never succeeded in fertilising C. tridentatum. If
there be not, then, an arrangement of the reproductive structures, such as
I have indicated, how can the different results in M. Neumann's experiments
and mine be accounted for? However, as you have examined many flowers of
both A. luteola and Loddigesii, such a difference in the ovulary or
placental structures could scarcely have escaped your observation. But, be
this as it may, the--to me at least--demonstrated fact still remains, that
certain flowers of A. Loddigesii are capable of fertilisation, and that,
though there are good grounds for supposing that important physiological
changes are going on in the sexual phenomena of this species, there is no
evidence whatever for supposing that external morphological changes have so
masked certain individuals as to prevent their recognition.
I would now, sir, in conclusion beg you to excuse me for this infringement
upon your valuable time, as I have been induced to write you in the belief
that you have had negative results from other experimenters, before you
ventured to propose your theoretical explanation, and consequently that you
have been unknowingly led into error. I will continue, as opportunities
present themselves, to examine the many peculiarities you have pointed out
in this as well as others of the Orchid family; and at present I am looking
forward with anxiety for the maturation of the ovary of A. Loddigesii,
which will bear testimony to the veracity of the remarks I have ventured to
lay before you.
LETTER 632. TO J.D. HOOKER.
Down, 18th [November 1862].
Strange to say, I have only one little bother for you to-day, and that is
to let me know about what month flowers appear in Acropera Loddigesii and
luteola; for I want extremely to beg a few more flowers, and if I knew the
time I would keep a memorandum to remind you. Why I want these flowers is
(and I am much alarmed) that Mr. J. Scott, of Bot. Garden of Edinburgh (do
you know anything of him?) has written me a very long and clever letter, in
which he confirms most of my observations; but tells me that with much
difficulty he managed to get pollen into orifice, or as far as mouth of
orifice, of six flowers of A. Loddigesii (the ovarium of which I did not
examine), and two pods set; one he gathered, and saw a very few ovules, as
he thinks, on the large and mostly rudimentary placenta. I shall be most
curious to hear whether the other pod produces a good lot of seed. He says
he regrets that he did not test the ovules with chemical agents: does he
mean tincture of iodine? He suggests that in a state of nature the viscid
matter may come to the very surface of stigmatic chamber, and so pollen-
masses need not be inserted. This is possible, but I should think
improbable. Altogether the case is very odd, and I am very uneasy, for I
cannot hope that A. Loddigesii is hermaphrodite and A. luteola the male of
the same species. Whenever I can get Acropera would be a very good time
for me to look at Vanda in spirits, which you so kindly preserved for me.
LETTER 633. TO J. SCOTT.
(633/1. The following is Darwin's reply to the above letter from Scott.
In the first edition of "Fertilisation of Orchids" (page 209) he assumed
that the sexes in Acropera, as in Catasetum, were separate. In the second
edition (page 172) he writes: "I was, however, soon convinced of my error
by Mr. Scott, who succeeded in artificially fertilising the flowers with
their own pollen. A remarkable discovery by Hildebrand (633/2. "Bot.
Zeitung," 1863 and 1865.), namely, that in many orchids the ovules are not
developed unless the stigma is penetrated by the pollen-tubes...explains
the state of the ovarium in Acropera, as observed by me." In regard to
this subject see Letter 608.)
Down, November 12th, 1862.
I thank you most sincerely for your kindness in writing to me, and for
[your] very interesting letter. Your fact has surprised me greatly, and
has alarmed me not a little, for if I am in error about Acropera I may be
in error about Catasetum. Yet when I call to mind the state of the
placentae in A. luteola, I am astonished that they should produce ovules.
You will see in my book that I state that I did not look at the ovarium of
A. Loddigesii. Would you have the kindness to send me word which end of
the ovarium is meant by apex (that nearest the flower?), for I must try and
get this species from Kew and look at its ovarium. I shall be extremely
curious to hear whether the fruit, which is now maturing, produces a large
number of good and plump seed; perhaps you may have seen the ripe capsules
of other Vandeae, and may be able to form some conjecture what it ought to
produce. In the young, unfertilised ovaria of many Vandeae there seemed an
infinitude of ovules. In desperation it occurs to me as just possible, as
almost everything in nature goes by gradation, that a properly male flower
might occasionally produce a few seeds, in the same manner as female plants
sometimes produce a little pollen. All your remarks seem to me excellent
and very interesting, and I again thank you for your kindness in writing to
me. I am pleased to observe that my description of the structure of
Acropera seems to agree pretty well with what you have observed. Does it
not strike you as very difficult to understand how insects remove the
pollinia and carry them to the stigmas? Your suggestion that the mouth of
the stigmatic cavity may become charged with viscid matter and thus secure
the pollinia, and that the pollen-tubes may then protrude, seems very
ingenious and new to me; but it would be very anomalous in orchids, i.e. as
far as I have seen. No doubt, however, though I tried my best, I shall be
proved wrong in many points. Botany is a new subject to me. With respect
to the protrusion of pollen-tubes, you might like to hear (if you do not
already know the fact) that, as I saw this summer, in the little imperfect
flowers of Viola and Oxalis, which never open, the pollen-tubes always come
out of the pollen-grain, whilst still in the anthers, and direct themselves
in a beautiful manner to the stigma seated at some little distance. I hope
that you will continue your very interesting observations.
LETTER 634. TO J. SCOTT.
Down, November 19th [1862].
I am much obliged for your letter, which is full of interesting matter. I
shall be very glad to look at the capsule of the Acropera when ripe, and
pray present my thanks to Mr. MacNab. (634/1. See Letter 608 (Lindley,
December 15th, 1861). Also "Fertilisation of Orchids," Edition II., page
172, for an account of the observations on Acropera which were corrected by
Scott.) I should like to keep it till I could get a capsule of some other
member of the Vandeae for comparison, but ultimately all the seeds shall be
returned, in case you would like to write any notice on the subject. It
was, as I said (634/2. Letter 633.), only "in desperation" that I
suggested that the flower might be a male and occasionally capable of
producing a few seeds. I had forgotten Gartner's remark; in fact, I know
only odds and ends of Botany, and you know far more. One point makes the
above view more probable in Acropera than in other cases, viz. the presence
of rudimentary placentae or testae, for I cannot hear that these have been
observed in the male plants. They do not occur in male Lychnis dioica, but
next spring I will look to male holly flowers. I fully admit the
difficulty of similarity of stigmatic chamber in the two Acroperas. As far
as I remember, the blunt end of pollen-mass would not easily even stick in
the orifice of the chamber. Your view may be correct about abundance of
viscid matter, but seems rather improbable. Your facts about female
flowers occurring where males alone ought to occur is new to me; if I do
not hear that you object, I will quote the Zea case on your authority in
what I am now writing on the varieties of the maize. (634/3. See "Animals
and Plants," Edition II., Volume I., page 339: "Mr. Scott has lately
observed the rarer case of female flowers on a true male panicle, and
likewise hermaphrodite flowers." Scott's paper on the subject is in
"Trans. Bot. Soc. Edinburgh," Volume VIII. See Letter 151, Volume I.) I
am glad to hear that you are now working on the most curious subject of
parthenogenesis. I formerly fancied that I observed female Lychnis dioica
seeded without pollen. I send by this post a paper on Primula, which may
interest you. (634/4. "Linn. Soc. Journal," 1862.) I am working on the
subject, and if you should ever observe any analogous case I should be glad
to hear. I have added another very clever pamphlet by Prof. Asa Gray.
Have you a copy of my Orchis book? If you have not, and would like one, I
should be pleased to send one. I plainly see that you have the true spirit
of an experimentalist and good observer. Therefore, I ask whether you have
ever made any trials on relative fertility of varieties of plants (like
those I quote from Gartner on the varieties of Verbascum). I much want
information on this head, and on those marvellous cases (as some Lobelias
and Crinum passiflora) in which a plant can be more easily fertilised by
the pollen of another species than by its own good pollen. I am compelled
to write in haste. With many thanks for your kindness.
LETTER 635. TO J. SCOTT.
Down, 20th [1862?].
What a magnificent capsule, and good Heavens, what a number of seeds! I
never before opened pods of larger orchids. It did not signify a few seed
being lost, as it would be hopeless to estimate number in comparison with
other species. If you sow any, had you not better sow a good many? so I
enclose small packet. I have looked at the seeds; I never saw in the
British orchids nearly so many empty testae; but this goes for nothing, as
unnatural conditions would account for it. I suspect, however, from the
variable size and transparency, that a good many of the seeds when dry (and
I have put the capsule on my chimney-piece) will shrivel up. So I will
wait a month or two till I get the capsule of some large Vandeae for
comparison. It is more likely that I have made some dreadful blunder about
Acropera than that it should be male yet not a perfect male. May there be
some sexual relation between A. Loddigesii and luteola; they seem very
close? I should very much like to examine the capsule of the unimpregnated
flower of A. Loddigesii. I have got both species from Kew, but whether we
shall have skill to flower them I know not. One conjectures that it is
imperfect male; I still should incline to think it would produce by seed
both sexes. But you are right about Primula (and a very acute thought it
was): the long-styled P. sinensis, homomorphically fertilised with
own-form pollen, has produced during two successive homomorphic generations
only long-styled plants. (635/1. In "Forms of Flowers," Edition II., page
216, a summary of the transmission of forms in the "homomorphic" unions of
P. sinensis is given. Darwin afterwards used "illegitimate" for
homomorphic, and "legitimate" for "heteromorphic" ("Forms of Flowers,"
Edition i., page 24).) The short-styled the same, i.e. produced
short-styled for two generations with the exception of a single plant. I
cannot say about cowslips yet. I should like to hear your case of the
Primula: is it certainly propagated by seed?
LETTER 636. TO J. SCOTT.
Down, December 3rd, [1862?].
What a capital observer you are! and how well you have worked the primulas.
All your facts are new to me. It is likely that I overrate the interest of
the subject; but it seems to me that you ought to publish a paper on the
subject. It would, however, greatly add to the value if you were to cover
up any of the forms having pistil and anther of the same height, and prove
that they were fully self-fertile. The occurrence of dimorphic and non-
dimorphic species in the same genus is quite the same as I find in Linum.
(636/1. Darwin finished his paper on Linum in December 1862, and it was
published in the "Linn. Soc. Journal" in 1863.) Have any of the forms of
Primula, which are non-dimorphic, been propagated for some little time by
seed in garden? I suppose not. I ask because I find in P. sinensis a
third rather fluctuating form, apparently due to culture, with stigma and
anthers of same height. I have been working successive generations
homomorphically of this Primula, and think I am getting curious results; I
shall probably publish next autumn; and if you do not (but I hope you will)
publish yourself previously, I should be glad to quote in abstract some of
your facts. But I repeat that I hope you will yourself publish. Hottonia
is dimorphic, with pollen of very different sizes in the two forms. I
think you are mistaken about Siphocampylus, but I feel rather doubtful in
saying this to so good an observer. In Lobelia the closed pistil grows
rapidly, and pushes out the pollen and then the stigma expands, and the
flower in function is monoecious; from appearance I believe this is the
case with your plant. I hope it is so, for this plant can hardly require a
cross, being in function monoecious; so that dimorphism in such a case
would be a heavy blow to understanding its nature or good in all other
cases. I see few periodicals: when have you published on Clivia? I
suppose that you did not actually count the seeds in the hybrids in
comparison with those of the parent-forms; but this is almost necessary
after Gartner's observations. I very much hope you will make a good series
of comparative trials on the same plant of Tacsonia. (636/2. See Scott in
"Linn. Soc. Journal," VIII.) I have raised 700-800 seedlings from
cowslips, artificially fertilised with care; and they presented not a
hair's-breadth approach to oxlips. I have now seed in pots of cowslip
fertilised by pollen of primrose, and I hope they will grow; I have also
got fine seedlings from seed of wild oxlips; so I hope to make out the
case. You speak of difficulties on Natural Selection: there are indeed
plenty; if ever you have spare time (which is not likely, as I am sure you
must be a hard worker) I should be very glad to hear difficulties from one
who has observed so much as you have. The majority of criticisms on the
"Origin" are, in my opinion, not worth the paper they are printed on. Sir
C. Lyell is coming out with what, I expect, will prove really good remarks.
(636/3. Lyell's "Antiquity of Man" was published in the spring of 1863.
In the "Life and Letters," Volume III., pages 8, 11, Darwin's
correspondence shows his deep disappointment at what he thought Lyell's
half-heartedness in regard to evolution. See Letter 164, Volume I.) Pray
do not think me intrusive; but if you would like to have any book I have
published, such as my "Journal of Researches" or the "Origin," I should
esteem it a compliment to be allowed to send it. Will you permit me to
suggest one experiment, which I should much like to see tried, and which I
now wish the more from an extraordinary observation by Asa Gray on
Gymnadenia tridentata (in number just out of Silliman's N. American
Journal) (636/4. In Gymnadenia tridentata, according to Asa Gray, the
anther opens in the bud, and the pollen being somewhat coherent falls on
the stigma and on the rostellum which latter is penetrated by the pollen-
tubes. "Fertilisation of Orchids," Edition II., page 68. Asa Gray's
papers are in "American Journal of Science," Volume XXXIV., 1862, and
XXXVI., 1863.); namely, to split the labellum of a Cattleya, or of some
allied orchis, remove caudicle from pollen-mass (so that no loose grains
are about) and put it carefully into the large tongue-like rostellum, and
see if pollen-tubes will penetrate, or better, see if capsule will swell.
Similar pollen-masses ought to be put on true stigmas of two or three other
flowers of same plants for comparison. It is to discover whether rostellum
yet retains some of its primordial function of being penetrated by pollen-
tubes. You will be sorry that you ever entered into correspondence with
me. But do not answer till at leisure, and as briefly as you like. My
handwriting, I know, is dreadfully bad. Excuse this scribbling paper, as I
can write faster on it, and I have a rather large correspondence to keep
up.
LETTER 637. TO J. SCOTT.
Down, January 21st, 1863.
I thank you for your very interesting letter; I must answer as briefly as I
can, for I have a heap of other letters to answer. I strongly advise you
to follow up and publish your observations on the pollen-tubes of orchids;
they promise to be very interesting. If you could prove what I only
conjectured (from state of utriculi in rostellum and in stigma of Catasetum
and Acropera) that the utriculi somehow induce, or are correlated with,
penetration of pollen-tubes you will make an important physiological
discovery. I will mention, as worth your attention (and what I have
anxiously wished to observe, if time had permitted, and still hope to do)--
viz., the state of tissues or cells of stigma in an utterly sterile hybrid,
in comparison with the same in fertile parent species; to test these cells,
immerse stigmas for 48 hours in spirits of wine. I should expect in
hybrids that the cells would not show coagulated contents. It would be an
interesting discovery to show difference in female organs of hybrids and
pure species. Anyhow, it is worth trial, and I recommend you to make it,
and publish if you do. The pollen-tubes directing themselves to stigma is
also very curious, though not quite so new, but well worth investigation
when you get Cattleya, etc., in flower. I say not so new, for remember
small flowers of Viola and Oxalis; or better, see Bibliography in "Natural
History Review," No. VIII., page 419 (October, 1862) for quotation from M.
Baillon on pollen-tubes finding way from anthers to stigma in Helianthemum.
I should doubt gum getting solid from [i.e. because of] continued
secretion. Why not sprinkle fresh plaster of Paris and make impenetrable
crust? (637/1. The suggestion that the stigma should be covered with a
crust of plaster of Paris, pierced by a hole to allow the pollen-tubes to
enter, bears a resemblance to Miyoshi's experiments with germinating pollen
and fungal spores. See "Pringsheim's Jahrbucher," 1895; "Flora," 1894.)
You might modify experiment by making little hole in one lower corner, and
see if tubes find it out. See in my future paper on Linum pollen and
stigma recognising each other. If you will tell me that pollen smells the
stigma I will try and believe you; but I will not believe the Frenchman (I
forget who) who says that stigma of Vanilla actually attracts mechanically,
by some unknown force, the solid pollen-masses to it! Read Asa Gray in 2nd
Review of my Orchis book on pollen of Gymnadenia penetrating rostellum. I
can, if you like, lend you these Reviews; but they must be returned. R.
Brown, I remember, says pollen-tubes separate from grains before the lower
ends of tubes reach ovules. I saw, and was interested by, abstract of your
Drosera paper (637/2. A short note on the irritability of Drosera in the
"Trans. Bot. Soc. Edin." Volume VII.); we have been at very much the same
work.
LETTER 638. TO J. SCOTT.
Down, February 16th [1863].
Absence from home has prevented me from answering you sooner. I should
think that the capsule of Acropera had better be left till it shows some
signs of opening, as our object is to judge whether the seeds are good; but
I should prefer trusting to your better judgment. I am interested about
the Gongora, which I hope hereafter to try myself, as I have just built a
small hot-house.
Asa Gray's observations on the rostellum of Gymnadenia are very imperfect,
yet worth looking at. Your case of Imatophyllum is most interesting
(638/1. A sucker of Imatophyllum minatum threw up a shoot in which the
leaves were "two-ranked instead of four-ranked," and showed other
differences from the normal.--"Animals and Plants," Edition II., Volume I.,
page 411.); even if the sport does not flower it will be worth my giving.
I did not understand, or I had forgotten, that a single frond on a fern
will vary; I now see that the case does come under bud-variation, and must
be given by me. I had thought of it only as proof [of] inheritance in
cryptogams; I am much obliged for your correction, and will consult again
your paper and Mr. Bridgeman's. (638/2. The facts are given in "Animals
and Plants," Edition II., Volume I., page 408.) I enclose varieties of
maize from Asa Gray. Pray do not thank me for trusting you; the thanks
ought to go the other way. I felt a conviction after your first letter
that you were a real lover of Natural History.
If you can advance good evidence showing that bisexual plants are more
variable than unisexual, it will be interesting. I shall be very glad to
read the discussion which you are preparing. I admit as fully as any one
can do that cross-impregnation is the great check to endless variability;
but I am not sure that I understand your view. I do not believe that the
structure of Primula has any necessary relation to a tendency to a
dioecious structure, but seeing the difference in the fertility of the two
forms, I felt bound unwillingly to admit that they might be a step towards
dioeciousness; I allude to this subject in my Linum paper. (638/3. "Linn.
Soc. Journal," 1863.) Thanks for your answers to my other queries. I
forgot to say that I was at Kew the other day, and I find that they can
give me capsules of several Vandeae.
LETTER 639. TO J. SCOTT.
Down, March 24th [1863].
Your letter, as every one you have written, has greatly interested me. If
you can show that certain individual Passifloras, under certain known or
unknown conditions of life, have stigmas capable of fertilisation by pollen
from another species, or from another individual of its own species, yet
not by its own individual pollen (its own individual pollen being proved to
be good by its action on some other species), you will add a case of great
interest to me; and which in my opinion would be quite worth your
publication. (639/1. Cases nearly similar to those observed by Scott were
recorded by Gartner and Kolreuter, but in these instances only certain
individuals were self-impotent. In "Animals and Plants," Edition II.,
Volume II., page 114, where the phenomenon is fully discussed, Scott's
observations ("Trans. Bot. Soc. Edin." 1863) are given as the earliest,
except for one case recorded by Lecoq ("Fecondation," 1862). Interesting
work was afterwards done by Hildebrand and Fritz Muller, as illustrated in
many of the letters addressed to the latter.) I always imagined that such
recorded cases must be due to unnatural conditions of life; and think I
said so in the "Origin." (639/2. See "Origin of Species," Edition I.,
page 251, for Herbert's observations on self-impotence in Hippeastrum. In
spite of the uniformness of the results obtained in many successive years,
Darwin inferred that the plants must have been in an "unnatural state.") I
am not sure that I understand your result, [nor] whether it means what I
have above obscurely expressed. If you can prove the above, do publish;
but if you will not publish I earnestly beg you to let me have the facts in
detail; but you ought to publish, for I may not use the facts for years. I
have been much interested by what you say on the rostellum exciting pollen
to protrude tubes; but are you sure that the rostellum does excite them?
Would not tubes protrude if placed on parts of column or base of petals,
etc., near to the stigma? Please look at the "Cottage Gardener" (or
"Journal of Horticulture") (639/3. "Journal of Horticulture" and "Cottage
Gardener," March 31st, 1863. A short note describing Cruger's discovery of
self-fertilisation in Cattleya, Epidendrum, etc., and referring to the work
of "an excellent observer, Mr. J. Scott." Darwin adds that he is convinced
that he has underrated the power of tropical orchids occasionally to
produce seeds without the aid of insects.) to be published to-morrow week
for letter of mine, in which I venture to quote you, and in which you will
see a curious fact about unopened orchid flowers setting seed in West
Indies. Dr. Cruger attributes protrusion of tubes to ants carrying
stigmatic secretion to pollen (639/4. In Cruger's paper ("Linn. Soc.
Journ." VIII., 1865; read March 3rd 1864) he speaks of the pollen-masses in
situ being acted on by the stigmatic secretion, but no mention is made of
the agency of ants. He describes the pollen-tubes descending "from the
[pollen] masses still in situ down into the ovarian canal."); but this is
mere hypothesis. Remember, pollen-tubes protrude within anther in Neottia
nidus-avis. I did think it possible or probable that perfect fertilisation
might have been effected through rostellum. What a curious case your
Gongora must be: could you spare me one of the largest capsules? I want
to estimate the number of seed, and try my hand if I can make them grow.
This, however, is a foolish attempt, for Dr. Hooker, who was here a day or
two ago, says they cannot at Calcutta, and yet imported species have seeded
and have naturally spread on to the adjoining trees! Dr. Cruger thinks I
am wrong about Catasetum: but I cannot understand his letter. He admits
there are three forms in two species; and he speaks as if the sexes were
separate in some and that others were hermaphrodites (639/5. Cruger
("Linn. Soc. Journal," VIII., page 127) says that the apparently
hermaphrodite form is always sterile in Trinidad. Darwin modified his
account in the second edition of the orchid book.); but I cannot understand
what he means. He has seen lots of great humble-bees buzzing about the
flowers with the pollinia sticking to their backs! Happy man!! I have the
promise, but not yet surety, of some curious results with my homomorphic
seedling cowslips: these have not followed the rule of Chinese Primula;
homomorphic seedlings from short-styled parent have presented both forms,
which disgusts me.
You will see that I am better; but still I greatly fear that I must have a
compulsory holiday. With sincere thanks and hearty admiration at your
powers of observation...
My poor P. scotica looks very sick which you so kindly sent me. (639/6.
Sent by Scott, January 6th, 1863.)
LETTER 640. TO J. SCOTT.
April 12th [1863].
I really hardly know how to thank you enough for your very interesting
letter. I shall certainly use all the facts which you have given me (in a
condensed form) on the sterility of orchids in the work which I am now
slowly preparing for publication. But why do you not publish these facts
in a separate little paper? (640/1. See Letter 642, note, for reference
to Scott's paper.) They seem to me well worth it, and you really ought to
get your name known. I could equally well use them in my book. I
earnestly hope that you will experiment on Passiflora, and let me give your
results. Dr. A. Gray's observations were made loosely; he said in a letter
he would attend this summer further to the case, which clearly surprised
him much. I will say nothing about the rostellum, stigmatic utriculi,
fertility of Acropera and Catasetum, for I am completely bewildered: it
will rest with you to settle these points by your excellent observations
and experiments. I must own I never could help doubting Dr. Hooker's case
of the poppy. You may like to hear what I have seen this morning: I found
(640/2. See Letter 658.) a primrose plant with flowers having three
pistils, which when pulled asunder, without any tearing, allowed pollen to
be placed on ovules. This I did with three flowers--pollen-tubes did not
protrude after several days. But this day, the sixteenth (N.B.--primulas
seem naturally slowly fertilised), I found many tubes protruded, and, what
is very odd, they certainly seemed to have penetrated the coats of the
ovules, but in no one instance the foramen of the ovule!! I mention this
because it directly bears on your explanation of Dr. Cruger's case.
(640/3. Cruger's case here referred to is doubtless the cleistogamic
fertilisation of Epidendrum, etc. Scott discusses the question of
self-fertilisation at great length in a letter to Darwin dated April, and
obviously written in 1863. In Epidendrum he observed a viscid matter
extending from the stigmatic chamber to the anther: pollen-tubes had
protruded from the anther not only where it was in contact with the viscid
matter, but also from the central part, and these spread "over the anterior
surface of the rostellum downward into the stigma." Cruger believed the
viscid matter reaching the anther was a necessary condition for the
germination of the pollen-grains. Scott points out that the viscid matter
is produced in large quantity only after the pollen-grains have penetrated
the stigma, and that it is, in fact, a consequence, not a preliminary to
fertilisation. He finally explains Cruger's case thus: "The greater
humidity and equability of temperature consequent on such conditions [i.e.
on the flowers being closed] is, I believe, the probable cause of these
abnormally conditioned flowers so frequently fertilising themselves."
Scott also calls attention to the danger of being deceived by fungal hyphae
in observations on germination of pollen.) I believe that your explanation
is right; I should never have thought of it; yet this was stupid of me, for
I remember thinking that the almost closed imperfect flowers of Viola and
Oxalis were related to the protrusion of the pollen-tubes. My case of the
Aceras with the aborted labellum squeezed against stigma supports your
view. (640/4. See "Fertilisation of Orchids," Edition II., page 258: the
pollen germinated within the anther of a monstrous flower.) Dr. Cruger's
notion about the ants was a simple conjecture. About cryptogamic
filaments, remember Dr. C. says that the unopened flowers habitually set
fruit. I think that you will change your views on the imperfect flowers of
Viola and Oxalis...
LETTER 641. (?)
LETTER 642. TO J. SCOTT.
May 2nd [1863].
I have left home for a fortnight to see if I can, with little hope, improve
my health. The parcel of orchid pods, which you have so kindly sent me,
has followed me. I am sure you will forgive the liberty which I take in
returning you the postage stamps. I never heard of such a scheme as that
you were compelled to practise to fertilise the Gongora! (642/1. See
"Fertilisation of Orchids," Edition, II., page 169. "Mr. Scott tried
repeatedly, but in vain, to force the pollen-masses into the stigma of
Gongora atro-purpurea and truncata; but he readily fertilised them by
cutting off the clinandrum and placing pollen-masses on the now exposed
stigma.") It is a most curious problem what plan Nature follows in this
genus and Acropera. (642/2. In the "Fertilisation of Orchids," Edition
II., page 169, Darwin speculates as to the possible fertilisation of
Acropera by an insect with pollen-masses adhering to the extremity of its
abdomen. It would appear that this guess (which does not occur in the
first edition) was made before he heard of Cruger's observation on the
allied genus Gongora, which is visited by a bee with a long tongue, which
projects, when not in use, beyond and above the tip of the abdomen. Cruger
believes that this tongue is the pollinating agent. Cruger's account is in
the "Journal of the Linn. Soc." VIII., 1865, page 130.) Some day I will
try and estimate how many seeds there are in Gongora. I suppose and hope
you have kept notes on all your observations on orchids, for, with my
broken health and many other subjects, I do not know whether I shall ever
have time to publish again; though I have a large collection of notes and
facts ready. I think you show your wisdom in not wishing to publish too
soon; a young author who publishes every trifle gets, sometimes unjustly,
to be disregarded. I do not pretend to be much of a judge; but I can
conscientiously say that I have never written one word to you on the merit
of your letters that I do not fully believe in. Please remember that I
should very much wish for a copy of your paper on sterility of individual
orchids (642/3. "On the Individual Sterility and Cross-Impregnation of
Certain Species of Oncidium." [Read June 2nd, 1864.] "Linn. Soc. Journal,"
VIII., 1865. This paper gives a full account of the self-sterility of
Oncidium in cases where the pollen was efficient in fertilising other
individuals of the same species and of distinct species. Some of the facts
were given in Scott's paper, "Experiments on the Fertilisation of Orchids
in the Royal Botanic Garden of Edinburgh," published in the "Proc. Bot.
Soc. Edinb." 1863. It is probably to the latter paper that Darwin refers.)
and on Drosera. (642/4. "Trans. Bot. Soc. Edinburgh," Volume VII.)
Thanks for [note] about Campanula perfoliata. I have asked Asa Gray for
seeds, to whom I have mentioned your observations on rostellum, and asked
him to look closer to the case of Gymnadenia. (642/5. See "Fertilisation
of Orchids," Edition II., page 68.) Let me hear about the sporting
Imatophyllum if it flowers. Perhaps I have blundered about Primula; but
certainly not about mere protrusion of pollen-tubes. I have been idly
watching bees of several genera and diptera fertilising O. morio at this
place, and it is a very pretty sight. I have confirmed in several ways the
entire truth of my statement that there is no vestige of nectar in the
spur; but the insects perforate the inner coat. This seems to me a curious
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